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TABLE 3-5 Summary and description of reference site data used in the analysis
Road type State Description Miles Mile- All crashes Fatal and Average
years injury AADT
crashes
Two-lane Pennsylvania Untreated two-lane 170 1690 2332 455 4517
roadways roadway sections
New York Untreated two-lane 182 1683 2400 1211 4300
roadway sections
New Jersey Before-period data of 191 1337 8737 3338 12737
treatment sites
Illinois Before-period data of 460 2755 2783 706 22850
treatment sites
Four-lane Missouri Before-period data of 1826 14801 30274 9642 13560
freeways treatment sites
Pennsylvania Before-period data of 779 3807 5750 741 24995
treatment sites
New York Untreated two-lane 122 1098 3387 1497 12870
roadway sections
Wisconsin Before-period data of 456 2280 10831 2714 20900
treatment sites
Four-lane Pennsylvania Before-period data of 106 503 725 126 13810
divided treatment sites
expressways
Wisconsin Before-period data of 145 725 2174 361 11770
treatment sites
PRPMs. This meant that data availability for the purpose of TABLE 3-6 Crash data variables obtained from each state
calibrating the SPFs would be nonexistent for the period after Category Variable
nonselective installations were implemented and could be Time variables Crash date
scarce toward the completion of the nonselective installa-
Crash time
tions statewide. To calibrate the SPFs for these later years, a
Environmental variables Road surface condition
comparison group of sites was identified that consisted of as-
yet untreated locations or locations on which PRPMs had Weather condition
been installed prior to the beginning of the study period. The Light condition
comparison group accounted for time trends throughout the Crash-related variables Impact type
SPF calibration period. Special attention was given by the Crash severity
research team when selecting roadways to avoid any road- Initial direction
ways near PRPM locations in order to minimize the influence Vehicle maneuver
of any spillover or migration effects. Alignment
Because of the widespread implementation of PRPMs in
Location type (intersection vs. nonintersection)
Illinois, it was not possible to select a suitable comparison
Roadway variables Route number
group of sites in this state. Thus, for this state, SPFs were fit-
ted to the data for the later years of the after period to develop Milepost or reference point and offset
time trend factors for these later years.
However, in Wisconsin, the widespread implementation of TABLE 3-7 Crash data period, source,
PRPMs on four-lane freeways and expressways during 1999 and roadway referencing system
resulted in very limited comparison group data for a total of State Period Source Referencing System
43 miles of four-lane freeway. To address this constraint and to Illinois 19912000 Highway Safety County, route, milepoint
account for time trends in more recent years (i.e., 19982000), Information System
the research team collected additional data for urban Interstate (HSIS)
highways in Madison County, Wisconsin. Missouri 19912000 Missouri DOT Route, milepoint
New Jersey 19911998 Internet/New Jersey Route, milepoint
(excluding DOT
1996)
3.2.3 Crash Data
New York 19912000 New York DOT Reference marker
Pennsylvania 19912001 Pennsylvania DOT County, route, segment, offset
The crash databases obtained from each state contained
the variables listed in Table 3-6. Table 3-7 shows the period Wisconsin 19942001 Wisconsin DOT Route, reference point, offset
